The long-term goal of the proposed research is to understand how the functional divisions of auditory cortex relate to the analysis of complex sounds. Investigation will focus on the processing of intensity and temporal information in the auditory central nervous system (CNS) of the cat. The anatomical connections and architectonic parcellation of this system is well studied but much less is known about its functional organization. Two cortical regions: primary auditory cortex (AI) and posterior auditory field (PAF) will be the subject of physiological studies with these specific aims: l) to investigate the relationship between the response properties of geniculocortical afferents and the cortical cells to which the afferents provide input, and 2) to investigate the subconical organization of those afferents. Electrophysiological recordings will be acquired in either hemisphere of anesthetized cats under contralateral ear stimulation. For aim 1, single cortical neurons will be characterized in terms of their intensity tuning or temporal integration properties. The response of the cortical cells will then be pharmacologically silenced, which will enable recording from thalamic afferents in the same electrode penetration. For aim 2, recordings will be made from the cell bodies of afferents while simultaneously recording from cortical cells to which they provide input. The afferent recordings will be compared to the cortical recordings and interpreted in terms of the cortical transformations of afferent inputs. The subcortical organization of the inputs to PAF and AI will be compared and interpreted in terms of parallel and hierarchical organization of function. The results of these investigations will be relevant to understanding the basis of auditory perception and disturbances in auditory perception due to acquired lesions, developmental learning impairments, and schizophrenia.